1. Field of the Invention
This invention relates to alkoxy-functional room temperature vulcanizing (RTV) compositions, curable in the presence of moisture, comprising polymers containing on average at least 1.2 alkoxysilyl chain terminations per molecule, a tetraalkoxytitanium compound containing on average greater than 90 mole percent of the alkoxy groups as tertiary amyloxy groups, a filler, and an alkoxysilane. The addition of these components in amounts to satisfy defined molar ratios provide alkoxy-functional RTV compositions having both improved storage stability and improved green strength upon curing.
2. Background Information
Polyorganosiloxane compositions which cure to elastomeric materials at room temperature are well known. Such compositions can be obtained by mixing polydiorganosiloxanes having reactive groups, such as silanol groups, with silane crosslinking agents, for example, alkoxysilanes, acetoxysilanes, oximosilanes, or aminosilanes. Compositions comprising these ingredients can then be cured by exposure to atmospheric moisture at room temperature.
Moisture curable compositions are well known for their use as sealants. In certain applications, such as the manufacture of insulated glass window units, it is necessary to use a sealant which can quickly develop green strength so that elements of a construction can be formed and will maintain the desired configuration even if handled, packaged, and shipped after relatively short cure times, without showing permanent deformation.
Sealant compositions which can quickly develop green strength include silicone sealant compositions which evolve acetic acid, ketoximes, or amines as by-products during cure. These by-products have unpleasant odors and may corrode sensitive metals or plastics. The use of other compositions which would not have these properties would therefore be beneficial. One potential alternative to these compositions is an alkoxy-functional RTV composition containing tetraalkoxytitanium compounds derived from primary or secondary alcohols and liberating alcohol during cure. However, the alkoxy-functional RTV compositions containing these tetraalkoxytitanium compounds derived from primary or secondary alcohols do not have sufficient green strength for applications requiring packing and shipping of assembled components soon after manufacture.
The present inventors have unexpectedly determined that alkoxy-functional RTV compositions have improved green strength upon curing and improved storage stability when on average greater than 90 mole percent of the alkoxy groups of the tetraalkoxytitanium compound are tertiary-amyloxy (t-amyloxy) groups and the components are added in amounts to satisfy defined molar ratios. The term "green strength" as defined herein means a high-modulus skin of sufficient strength that elements of a construction can be formed and will maintain the desired configuration even if handled, packaged, and shipped after relatively short cure times, without showing permanent deformation. The term "storage stability" as defined herein means that the uncured composition maintains its rheology during storage and when cured, the green strength is essentially the same or improved relative to the green strength of the composition prior to storage.
One objective of this invention is to prepare an alkoxy-functional RTV composition having improved green strength upon curing. Another objective of this invention is to prepare an alkoxy-functional RTV composition having improved storage stability.